Fly{40 s eye lens process

ABSTRACT

An improved structure and method for the electrostatic lens array of a fly&#39;&#39;s eye lens in an electron beam device resulting in precise parallel spacing of the planar lens electrodes as well as precise axial alignment of the arrays of openings in the lens electrodes.

United States Patent Hooker 1 Dec. 5, 1972 [54] FLY'S EYE LENS PROCESS[72] Inventor: John M. Hooker, Owensboro, Ky.

[73] Assignee: General Electric Company [22] Filed: Dec. 18, 1969 [21]Appl. No.: 886,218

[52] US. Cl. ..29/592, 29/25.16, 29/25.17, 29/25.14, 29/447, 29/622,29/471.1, 313/348 [51] Int. Cl ..B23k 21/00, B23p 11/02 [58] Field ofSearch ..29/592, 622, 25.16, 471.1, 29/472.3, 472.7, 25.17, 447;313/348, 262,

[56] References Cited UNITED STATES PATENTS 2,654,940 10/1953 Law..29/447 X 3,284,655 ll/l966 Oess ..313/348 X 3,435,274 3/1969 Miller..313/348 3,436,585 4/1969 Murakami 2,463,416 3/1949 Nordsieck 2,508,9795/1950 Van Gessel 2,740,913 4/1956 Majkrzak 3,336,664 8/1967 Hankins..29/622 Primary ExaminerJohn F. Campbell Assistant Examiner-Robert W.Church Attorney-Nathan J. Comfeld, John P. Taylor, Frank L. Neuhauser,Oscar B. Waddell and Joseph B. Forman [5 7] ABSTRACT An improvedstructure and method for the electrostatic lens array of a flys eye lensin an electron beam device resulting in precise parallel spacing of theplanar lens electrodes as well as precise axial alignment of the arraysof openings in the lens electrodes.

9 Claims, 3 Drawing Figures PATENTED 5 I972 FIG ATTACH PLANAR MEMBERS TOSUPPORT RINGS AT NON-AMBIENT TEMPERATURE BRING SUBASSEMBLIES T0 AMBIENTTEMPERATURE r0 TENSION PLANAR MEMBERS.

AXIALLY ALIGN OPENINGS IN ADJACENT PLANAR MEMBERS.

INVENTOR JOHN M. HOOKER,

ATTACH ADJACENT SUPPORT BY ms ATTORNEY.

RINGS WHILE MAINTAINING AXIAL ALIGNMENT.

FLY 'S EYE LENS PROCESS BACKGROUND OF THE INVENTION This inventionrelates to an electron beam tube having a compound lens systemcomprising a plurality of focusing and deflecting electrodes in a matrixfor precise control of the electron beam. More particularly it relatesto a novel electrostatic focusing lens array structure for the tube andto a method of constructing the lens structure.

A system for precise control of an electron beam is described in a paperby S.P. Newberry titled Problems of Microspace Information Storage,appearing in the Fourth Electron Beam Symposium (March 29-30, 1962),published by Alloyd Electronics Corporation, Boston, Massachusetts, andagain in The Flys Eye LensA Novel Electron Optical Component for UseWith Large Capacity Random Access Memories by SF. Newberry in Volume 29of the American Federation of Information Processing Societies,Conference Proceedings, published by Spartan Books, Washington, DC.(November 1966). The system therein described comprises an ultrahighdensity memory wherein impingement of an electron beam on a storagemedium is controlled by an objective lens made up of a matrix of minuteelectron optical lenses, therein referred to as lenslets. This matrix oflenses is superficially similar in appearance to the compound eye of anordinary housefly and therefor is designated a Flys Eye Lens. Byutilizing coarse deflection of the electron beam so as to strike only adesired lens of the matrix, the lens, thus struck, positions the beam toultimately impinge upon the storage medium at the desired point.Although the coarsely deflected beam may not strike the desired lens atdead center, the accuracy with which the beam strikes the storage mediumremains unimpaired so long as even a portion of the beam strikes thedesired lens.

Briefly, the planar array of lenses comprises three parallel plates witha plurality of axially aligned openings therein to form an array ofelectrostatic lenses for fine focusing and, immediately following eachlens, a set of X and Y deflection plates for fine deflection. Theresultant ultra high resolution electron beam tube can be used, forexample, in apparatus for the fabrication of integrated circuits such asdescribed and claimed in copending application Ser. No. 671,353, filedSept. 28, 1967, now US. Pat. No. 3,491,236, and assigned to the assigneeof this invention.

It has been found that the mounting of the three parallel platescomprising the electrostatic focusing lenses in exact parallelrelationship as well as correct axial alignment with regard to therespective openings in the plates is difficult. The plates tend to sagslightly thus disturbing the electron optics of the lenses including theuniformity of the foci of the respective lenses.

It is therefor an object of this invention to provide an improvedelectrostatic lens structure for a compound lens system with preciseparallel spacing of the planar metallic members comprising theelectrodes of the lenses as well as precise axial alignment of therespective openings in the planar members through which the beam passes.

It is another object of this invention to provide a method of assemblingan improved electrostatic lens structure for a compound lens system.

These and other objects will be apparent fromthe drawings and thedescription.

In accordance with a preferred embodiment of the invention, the lensstructure comprises an assembly of parallel, spaced planar metallicmembers. Each of the members is attached to a metallic support ringhaving a coefficient of expansion different from that of the planarmember. The attachment of each planar member to a support ring is madeat a preselected temperature so that subsequent exposure to a secondselected temperature, such as, for example, the normal operatingtemperature of the lens structure, causes a tensioning of the planarmember. The openings in each planar member are axially aligned with. therespective openings of the other planar members comprising the lens.Alignment is maintained by the peripheral attachment of the respectivesupport members together. The invention will be further understood byreferring to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinalcross-sectional sketch illustrating a device using the lens structure ofthe invention.

FIG. 2 is an exploded isometric view of the lens structure.

FIG. 3 is a flow sheet of the method for constructing the lensstructure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 generally illustrates adevice in which the lens system of the invention may be used. A vacuumenclosure is generally indicated at 2 wherein a beam 4 of chargedparticles such as an electron beam produced by an electron emittingsource 6 is controllably deflected onto a target 20 such as asemiconductor wafer coated with an electron-sensitive resist material.

Beam 4 produced by electron source 6 passes through a beam limitingaperture 8 and is collimated by an electrostatic condenser lens 10. Thebeam is then coarsely deflected in the X and Y planes respectively, bydeflection plates 12a, 12b and 14a, 14b. The particular electron opticsused to direct the beam to each lens may, of course, be varied andoptimized using various structures and techniques forming no part of thepresent invention. The lens structure of the invention is generallyindicated at 30 in FIG. 1. The lens structure, which will be describedin more detail below, generally comprises three parallel plates 32, 42,and 52, each having an array of openings 28 therethrough in axialalignment to form an array of electrostatic lens.

Immediately following the lens structure is a fine deflection systemcomprising a first set of parallel bars immediately followed by a secondset of parallel bars at right angles to the first set of bars. The barsthus form a criss-cross array or lattice conforming spacially to theopenings in the lens plates to provide a fine X-Y deflection system foreach lens. The fine deflection system is more fully described in saidaforementioned US. patent application Ser. No. 671,353-Newberry, filedSept. 28, 1967, cross-reference to which is hereby made.

Referring now to FIG. 2, the construction of the electrostatic lens 30of the invention is more clearly illustrated. It should be noted thatthe openings 28 in the lens plate have been exaggerated in size forillustrative purposes. In actual construction, openings 28 may be sosmall they would be difficult to see with the naked eye. A circular lensplate 32 is mounted on a cylindrical portion 34 of a metallic supportring 36 having a generally horizontal outer support lip 38.

A second circular lens plate 42, of slightly larger diameter than lensplate 32, is mounted on cylindrical portion 44 of a metallic supportring 46. Cylindrical portion 44 is of slightly larger diameter thancylindrical portion 34 of support ring 36. Support ring 46 has agenerally horizontal outer support lip 48. The cylindrical portion 44 issomewhat shorter in length than cylindrical portion 34 of support ring36.

Circular lens plate 52, of slightly larger diameter than lens plate 42,is mounted on cylindrical portion 54 of support ring 56. Cylindricalportion 54 is of larger diameter and shorter length than correspondingcylindrical portion 44. Thus, as is apparent from the drawing, the threelens plates and corresponding support rings are dimensioned to fittogether in nesting relationship.

Since lens plates 32, 42, and 52 each forms one electrode of a threeelectrode electrostatic lens, the lens plates must be insulated from oneanother. Ceramic insulating cylinders 62 and 66 are therefore provided.Ceramic cylinders '62 and 66 are respectively sealed to the upper andlower surfaces of horizontal lip 48 of support ring 46. Theopposite endof each ceramic cylinder is fitted with respective flanges 64 and 68 forsubsequent attachment to support rings 36 and 56 as will be described.

In accordance with the preferred embodiment of the invention, thematerials chosen for the lens plates 32, 42, and 52, the support rings36, 46, and 56; flanges 64 and 68, and the ceramic insulators 62 and 66are selected to provide (a) a good ceramic to metal bond between themetallic support ring material and ceramic insulators as well as flanges64 and 68 with the ceramic insulator; (b) a coefficient of expansionmismatch between the metallic lens plates and the support ring;

and (c) a matching coefficient of expansion between the support ringsand flanges 64 and 68.

Thus as a specific example of materials selected in the preferredembodiment of the invention, support rings 36, 46, and 56 and flanges 64and 68 are made of titanium metal and insulating rings 62 and 66 aremade of fosterite ceramic. Excellent ceramic-to-metal bonds can beobtained with these materials following the method described and claimedin Beggs US. Pat. No. 2,857,663, issued Oct. 28, 1958 and assigned tothe assignee of this invention.

When the above materials are used, lens plates 32, 42, and 52 arepreferably made from molybdenum or stainless steel. Each of thesematerials is thermally mismatched with respect to the titanium supportrings for a specific purpose as will be hereinafter described.Furthermore, both of these lens plate material have machining andchemical etching characteristics which are satisfactory for theplacement of an accurately spaced array of openings therein withcontrolled.

dimensions.

As previously mentioned, each of the lens plates 32, 42, and 52, areprovided with an array of openings therethrough. The axis of theopenings in each lens plate are spaced apart in prearranged identicalfashion allowing the respective openings in the three lens plates to beaxially aligned upon subsequent assembly. Thus the parallel mounting ofthe lens plates, with their respective openings aligned, creates anarray of Einzel lenses. For the electron optics of these lenses to becorrect and repetitive requires specific and accurate spacing of thelens plates relative to one another as well as precise parallelrelationship. Little or no warpage or sagging of the plates can betolerated.

I For this reason the metal material used for the lens plates isdeliberately chosen to be thermally mismatched to the support ring sothat attachment at a temperature other than normal operating temperaturefollowed by a return to normal operating temperature will cause atensioning of the lens plate on its respective support ring. 7

Furthermore, to ensure the parallel relationship, the support rings 36,46, and56 preferably are pre-assembled before attachment of the lensplates and the respective end surfaces 39, 49, and 59 of the cylindricalportions of the support rings are machinedto exact parallelrelationship. This may be done, for example, by pre-attaching ceramicinsulators 62 and 66 having flanges 64 and 68 respectively attachedthereto to the upper and lower surfaces of horizontal portion 48 ofsupport ring 46. Upper support ring 36 and lower support ring 56 maythen be detachably affixed to support ring 46 via an appropriatereleasable bonding agent between horizontal portion 38 and flange 64,and horizontal portion 58 and flange 68. After the machining of cylinderends 39, 49, and 59, the three support rings are disassembledpreparatory to attachment of the lens plates to the support rings.

Following disassembly, each lens plate is suitably attached securely toits support ring such as by welding or the like. When, for example,molybdenum lens plates are used, the lens plate and the titanium supportring are placed in a low temperature environment such as, for example, aliquid nitrogen or acetone-dry ice bath and welded together while at adepressed temperature. Subsequent removal of the welded lensplate-support ring assembly from the low temperature environment resultsin a greater expansion of the titanium support ring because of thethermal mismatch of the materials thereby tensioning the molybdenumplate. The attachment process is repeated for each lens plate supportring assembly.

Alternatively, when stainless steel is selected as the material for thelens plate, the weld is made at an elevated temperature. In this case,the greater expansion of the stainless steel causes a tensioning of thelens plate upon subsequent cooling to normal operating temperature.

The term normal operating temperature is herein defined as thetemperature of the electrostatic lens structure itself in actualoperation in an electron beam tube which may vary from about 0C to about300C depending upon whether heating or cooling means are employed in thevicinity of the lens structure.

The term elevated temperature, therefore, is intended to define atemperature above normal operating temperature. It should be noted,however, thatthe elevated temperature need not be higher than 300C ifthe contemplated normal operating temperature is not to be that high.The contemplated normal operating temperature may vary with thematerials selected for the thermal mismatch. For example, a stainlesssteel lens plate is normally welded to a titanium support ring at 150C.Therefore, when the lens structure is to be operated at about roomtemperature, or at least below 150C, such materials can be used. If,however, higher operating temperatures are contemplated other materialcombinations must be used; for example, the molybdenum lensplatetitanium support ring previously described.

The term low temperature is intended to define a temperature belownormal operating temperature, i.e., a temperature below about 0C.

Following individual attachment of the respective lens plates to theirsupport rings, the electrostatic lens is assembled by placing the lensplate-support ring subassemblies on independently adjustable stagesunder a high power microscope to axially align the respective openingsin the lens plates. For convenience, it is preferred to align and attachtwo lens plate-support ring assemblies in a first step followed byalignment and attachment of the third lens plate-support ring assembly.

In accordance with the invention, the lens plate openings are axiallyaligned and, while maintaining alignment, the respective support ringsare rigidly secured about their peripheries. Thus the openings in lensplate 32 are axially aligned with the respective openings in lens plate42 and, while alignment is maintained, support ring 36 is secured tosupport ring 46 by welding or clamping horizontal lip 38 on support ring36 to flange 64 carried by ceramic insulator 62 attached to horizontallip 48 of support ring 46. By constructing both flange 64 and supportring 36 of the same metal, a weld can be made without danger ofdisturbing the precise axial alignment of the openings in the lens plateby localized heating and uneven expansion of the metals (if dissimilarmetals were used) at the weld junction.

Following alignment and attachment of lens plates 32 and 42, theopenings in lens plate 52 are similarly aligned to the partiallyassembled lens and attachment is made, via lip 58 on support ring 56 toflange 68 while maintaining the axial alignment.

It should be noted here that ceramic spacers 62 and 66 may alternativelybe mounted or sealed respectively to horizontal lips 38 and 58 ofsupport rings 36 and 56. In this embodiment flanges 64 and 68 would beattached to the opposite side of the respective spacers for subsequentattachment respectively to the upper and lower surfaces of lip 48.

Thus, precise axial alignment of the respective openings in all threelens plates is maintained by attachment of the lens plates to oneanother by materials of matching temperature coefiicient of expansion.Precise parallel spacing of the lens plates is achieved by attachment ofeach lens plate at a temperature other than normal operating temperatureto a support ring constructed of a material having a differenttemperature coefficient of expansion so that subsequent exposure of thelens plate support ring assembly to normal operating temperature willtension the lens plate on the support ring.

Although the invention has been described only with reference to apreferred embodiment, other embodiments within the scope of theinvention will be readily apparent to those skilled in the art. Theinvention,

therefore, is to be limited only by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. The method of assembling together in precise spaced parallelalignment an electrostatic lens structure comprising three planarmetallic members, each of said members having a plurality of spacedopenings therein axially alignable with the respective openings in anadjacent member, comprising:

a. peripherally attaching each of said members to a circular metallicsupport comprising a material having a non-matching thermal coefficientof expansion, said attachment being made at a preselected temperature sothat the respective expansion and contraction of the non-matchingmaterials at the normal operating temperature of the lens structureresult in a tensioning of said members,

b. axially aligning the respective openings in one of said members withthe respective openings in adjacent members, and

c. thereafter securing together the respective adjacent supports on saidaxially aligned members at points on said supports spaced from saidmembers.

2. The method of claim 1 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature.

3. The method of claim 1 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.

4. The method of assembling together in precise spaced parallelalignment an electrostatic lens structure comprising three planarmetallic members, each of said members having a plurality of spacedopenings therein axially alignable with the respective openings in anadjacent member, comprising:

a. removably assembling together three circular metallic supports forsaid members comprising a material having a non-matching thermalcoefiicient of expansion with respect to said members;

b. precisely grinding the surfaces on said supports to which saidmembers will be attached to form precisely parallel planes;

c. detaching said supports from one another;

d. peripherally attaching each of said members to one of said circularmetallic supports, said attachment being made at a preselectedtemperature so that the respective expansion and contraction of thenon-matching materials at the normal operating temperature of the lensstructure result in a tensioning of said members;

. axially aligning the respective openings in one of said members withthe respective openings in adjacent members; and

f. thereafter securing together the respective adjacent supports on saidaxially aligned members at points on said supports spaced from saidmembers.

5. The method of claim 4 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature.

6. The method of claim 4 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.

7. The method of assembling together in precise spaced parallelalignment an electrostatic lens structure comprising three planarmetallic members, each of said members having a plurality of spacedopenings therein axially alignable with the respective openings in anadjacent member, comprising:

a. peripherally attaching each of said members to a circular metallicsupport comprising a material having a non-matching thermal coefficientof expansion, said attachment being made at a preselected temperature sothat the respective expansion and contraction of the non-matchingmaterials at the normal operating temperature of the lens structureresult in a tensioning of said members, one of said supports having atleast one insulator thereon and a metallic flange on said insulatorinsulatively spaced from said one support;

b. axially aligning the respective openings in one of said members withthe respective openings in adjacent members; and

c. thereafter securing together the respective adjacent supports on saidaxially aligned members at points on said supports spaced from saidmembers; said support having said insulator thereon being secured to anadjacent support by said flange.

8. The method of claim 7 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature.

9. The method of claim 7 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,704,511 Da ed December 5, 1972 Inventor(s) John M. Hooker It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the Claims,- column 8, line 20, insert the following claims:

10. The method of Claim 7 wherein said supports and said flange comprisetitanium and said insulator comprises a ceramic bondable to saidtitanium.

of- Claim 7 wherein said adjacent support .is support by welding: aportion of said said flange.

ll. The method mounted to said one adjacent support to Signed and sealedthis let day of May 1973. v

(SEAL) Attest:

ROBERT GOTTSCHALK EDI-JARD I' -I. FLETCHER, JR. I

Commissioner of Patents Attesting Officer FORM PC4050 (10459) USCOMMDC60376 P69 U-S. GOVERNMENT PRINTING OFFICE 1 I969 0-355-33

1. The method of assembling together in precise spaced parallelalignment an electrostatic lens structure comprising three planarmetallic members, each of said members having a plurality of spacedopenings therein axially alignable with the respective openings in anadjacent member, comprising: a. peripherally attaching each of saidmembers to a circular metallic support comprising a material having anon-matching thermal coefficient of expansion, said attachment beingmade at a pre-selected temperature so that the respective expansion andcontraction of the non-matching materials at the normal operatingtemperature of the lens structure result in a tensioning of saidmembers, b. axially aligning the respective openings in one of saidmembers with the respective openings in adjacent members, and c.thereafter securing together the respective adjacent supports on saidaxially aligned members at points on said supports spaced from saidmembers.
 2. The method of claim 1 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature. 3.The method of claim 1 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.
 4. Themethod of assembling together in precise spaced parallel alignment anelectrostatic lens structure comprising three planar metallic members,each of said members having a plurality of spaced openings thereinaxially alignable with the respective openings in an adjacent member,comprising: a. removably assembling together three circular metallicsupports for said members comprising a material having a non-matchingthermal coefficient of expansion with respect to said meMbers; b.precisely grinding the surfaces on said supports to which said memberswill be attached to form precisely parallel planes; c. detaching saidsupports from one another; d. peripherally attaching each of saidmembers to one of said circular metallic supports, said attachment beingmade at a preselected temperature so that the respective expansion andcontraction of the non-matching materials at the normal operatingtemperature of the lens structure result in a tensioning of saidmembers; e. axially aligning the respective openings in one of saidmembers with the respective openings in adjacent members; and f.thereafter securing together the respective adjacent supports on saidaxially aligned members at points on said supports spaced from saidmembers.
 5. The method of claim 4 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature. 6.The method of claim 4 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.
 7. Themethod of assembling together in precise spaced parallel alignment anelectrostatic lens structure comprising three planar metallic members,each of said members having a plurality of spaced openings thereinaxially alignable with the respective openings in an adjacent member,comprising: a. peripherally attaching each of said members to a circularmetallic support comprising a material having a non-matching thermalcoefficient of expansion, said attachment being made at a preselectedtemperature so that the respective expansion and contraction of thenon-matching materials at the normal operating temperature of the lensstructure result in a tensioning of said members, one of said supportshaving at least one insulator thereon and a metallic flange on saidinsulator insulatively spaced from said one support; b. axially aligningthe respective openings in one of said members with the respectiveopenings in adjacent members; and c. thereafter securing together therespective adjacent supports on said axially aligned members at pointson said supports spaced from said members; said support having saidinsulator thereon being secured to an adjacent support by said flange.8. The method of claim 7 wherein each of said members comprisemolybdenum, each of said supports comprises titanium, and saidattachment of the member to the support is made at a low temperature. 9.The method of claim 7 wherein each of said members comprise stainlesssteel, each of said supports comprises titanium, and said attachment ofthe member to the support is made at an elevated temperature.